<£■ 


LIBRARY 
STATE  PLANT  BOARD 


Circular  No.  64. 


United  States  Department  of  Agriculture, 

BUREAU    OF    ENTOMOLOGY, 

L.  O.  HOWARD,   Entomologist. 


THE  COTTONY  MAPLE  SCALE. 

(Pulvinaria  innumerabilis  Rathvon.) 

By  J.  G.  Sanders,  Assistant. 

The  cottony  maple  scale  (Pulvinaria  innumerabilis  Rathv.)  at  ma- 
turity is  the  most  conspicuous  scale  insect  indigenous  to  the  United 
States,  and  has  received  much  attention  from  entomologists  and  hor- 
ticulturists on  account  of  its  occasional  abundance.  It  was  described 
in  1854  by  Dr.  S.  S.  Rathvon,  of  Lancaster,  Pa.,  who  gave  the  pest 
a  very  expressive  and  significant  specific  name.  Since  then  over  60 
articles  and  references  con- 
cerning this  species  have 
appeared  in  entomological 
literature^  besides  hosts  of 
others  in  newspapers  and 
other  periodicals.  Of  spe- 
cial worth  is  a  monograph 
of  the  species,  worked 
out  in  elaborate  form  by 
J.  D.  Putnam,  which  was 
published  in  the  Proceed- 
ings of  the  Davenport 
(Iowa)  Academy  of  Natural 
Sciences,  page  339  (1879). 
More  recently  in  Bulletin 
22,  new  series^  Division  of 
Entomolog}',  Dr.  L.  O. 
Howard  published  a  thorough  treatise  on  "The  Two  Most 
Abundant  Pulvinarias  on  Maple/'  giving  in  detail  the  distribution, 
food  plants,  and  life  history  of  the  cottony  maple  scale  and  the 
nearly  related  maple-leaf  scale,  illustrated  by  numerous  figures  of 
the  various  stages  of  each  species. 
53816°— Cir.  64—10 


Fig.  I.— Pulvinaria  innumerabilis:  Adult  females  in  position 
on  twigs,  with  egg  sacs.    Natural  size.    (From  Howard.) 


3 


fU 


Sporadic  outbreaks  of  this  scale  insect  in  various  parts  of  the  United 
States  have  been  reported  from  time  to  time  for  many  years  past,  but 
in  each  case  natural  enemies  have  subsequently  increased  with  suf- 
ficient rapidity  to  effectually  check  its  progress.  Recently  many 
reports  of  its  extreme  abundance  have  come  to  us  from  the  city  of 
Chicago  and  vicinity,  and  from  various  sections  of  Illinois,  Indiana, 
Wisconsin,  and  Iowa,  It  is  interesting  to  note  that  most  of  the  re- 
ports of  serious  injury  by  this  insect  come  from  those  States  or  por- 
tions of  States  north  of  the  fortieth  parallel,  where  it  seems  to  be 
attacked  by  fewer  parasites  than  in  the  southern  regions.  A  map  of 
its  distribution  prepared  by  the  author  from  locality  cards  shows 
that  it  is  distinctively  an  Upper  Austral  zone  species  but  occasionally 
reaches  the  Transition  zone. 

The  cottony  maple  scale  is  classified  in  the  soft,  unarmored  group 
(Xon-Diaspinae)  of  the  family  Coccidae,  and  does  not  differ  superfici- 
ally from  the  Lecaniums,  except  in  the  formation  of  an  ovisac  by  the 
female  of  the  Pulvinaria.  The  male  insect  is  a  very  small  and  deli- 
cate two-winged  fly  which  develops  its  latter  stage  under  a  glassy 
test  or  covering  and  emerges  late  in  August  or  early  in  September. 

FOOD    PLANTS. 

The  various  species  of  maples,  particularly  the  soft  maple  (Acer 
saccharinum),  including  the  box-elder  (Acer  negundo),  are  the  favorite 
food  plants  of  this  species.  The  writer  has,  however,  found  it  on  47 
different  species  of  trees,  shrubs,  and  vines,  including  various  species 
of  maple,  oak,  linden,  elm,  willow,  poplar,  beech,  hawthorn,  syca- 
more, locust,  hackberry,  osage-orange,  mulberry,  grape,  poison-ivy, 
apple,  pear,  plum,  peach,  currant,  gooseberry,  rose,  and  Virginia 
creeper.  It  is  possible  that  a  very  careful  study  will  prove  that  all 
these  infestations  are  not  referable  to  one  species,  but  that  other 
species  may  be  separated  just  as  the  maple-leaf  Pulvinaria  [P.  aceri- 
cola  (Walsh  and  Riley)]  and  the  osage-orange  Pulvinaria  [P.  maclurse 
("Kenn.,"  Fitch)],  once  considered  identical,  were  found  to  be  dis- 
tinct from  the  cottony  maple  scale. 

HABITS    AND    LIFE    HISTORY. 

The  large,  white,  ilocculent  masses,  resembling  popcorn  fastened  to 
the  twigs,  which  appear  on  infested  trees  during  the  month  of  June, 
are  the  cottony  (really  waxy)  ovisacs  of  the  female,  provided  for  the 
retention  of  the  eggs  after  oviposition  (fig.  1).  These  may  contain  as 
many  as  1,500  minute,  oval,  pale  reddish-yellow  eggs. 

The  larva  hatch  at  various  dates  from  June  1  to  August  15,  depend- 
ing on  the  latitude  and  exposure  to  the  sun's  rays.  After  remaining 
[Clr.  64.] 


in  the  ovisac  for  a  day  or  two,  they  swarm  over  the  twi<_r-,  instinc- 
tively migrating  toward  the  light,  and  settle  on  the  leaves  along  the 
midribs  and  veins,  always  preferring  the  under  surface  (fig.  2,  e). 
The  larvre  on  box-older  become  active  somewhat  in  advance  of  those 
on  maple.  This  difference  may  be  due  to  the  food,  but  it  musl  be 
remembered  that  the  shade  of  the  box-elder  is  less  dense  than  thai 
of  the  maple,  and  consequently  the  greater  amount  of  heal  and  lighl 
may  be  the  controlling  factor.  The  male  larvae,  when  fully  grown, 
assume  a  propupal  stage  from  which  they  pass  to  the  true  pupal 
stage  having  a  pinkish  hue.  In  a  few  days  the  winged  males  appear, 
but  remain  beneath  the  scale  for  two  or  three  days  before  emerging. 
The  females  at  this  time  have  a  few  dorsal  brownish  markings  and 
have  undergone  two  molts.     The  males  and  females  copulate  in  Sep- 


Fig.  2.—Pulvinaria  innumerabilis:  a,  Newly-hatched  young;  b,  female,  third  stage,  from  above;  c,  same, 
from  side;  d,  male,  third  stage;  e,  same,  natural  size,  on  leaf  and  petiole;  /,  same,  enlarged,  on  leaf 
petiole  showing  two  specimens  parasitized.     All  greatly  enlarged  except  c.    (From  Howard.) 

tember,  and  soon  afterward  a  small  proportion  of  the  females  migrate 
to  the  twigs,  where  they  insert  their  probosces  and  become  fixed  for 
the  remainder  of  their  existence,  meanwhile  changing  from  a  greenish 
color  to  buff  and  finally  brown,  with  a  slightly  tessellated  waxy  cov- 
ering.    In  this  condition  the  winter  is  passed  (fig.  3). 

When  the  sap  begins  to  flow  in  the  early  spring  the  female  grows 
rapidly,  mainly  because  of  the  rapid  development  of  great  numbers  of 
eggs  within  the  body.  In  May  or  early  June  the  ovisac  begins  to  form 
from  the  fine  waxy  threads  exuded  from  the  posterior  spinnerets, 
pushing  backward  and  upward  until  the  body  of  the  female  is  almost 
vertical  to  the  twig.  Meanwhile  the  ovisac  is  gradually  being  filled 
with  eggs,  which  hatch  and  undergo  all  the  changes  mentioned  above. 
Thus,  fortunately,  there  is  but  a  single  brood  each  year. 

[Cir.64.] 


PARASITES    AND    PREDACEOUS    ENEMIES. 


Notwithstanding  the  extreme  prolificacy  of  this  insect,  it  is  usually 
held  in  check  by  its  many  natural  enemies.  Doctor  Howard  has 
observed  the  English  sparrow  apparently  feeding  upon  the  full-grown 
scales.  The  twice-stabbed  ladybird  (Chilocorus  bivulnerus  Muls.)  is  a 
common  enemy  of  this  as  of  other  scale  insects,  particularly  in  its 
early  stages.  The  smaller,  similarly  marked  Hyperaspis  binotata  Say 
(fig.  4)  and  //.  signata  Melsh.  are  also  valuable  enemies  of  this 
species.  The  writer  found  in  the  severely  infested  parks  and  cemeteries 
in  Chicago  that  the  egg-contents  of  80  to  85  per  cent  of  the  cottony 
ovisacs  had  been  destroyed  by  the  white  mealy  larvae  of  Hyperaspis. 
These  larvae  enter  and  devour  the  entire  contents  of  one  ovisac  after 
another  without  destroying  its  form,  so  that  only  an  examination  will 
reveal  the  empty  ones. 

The  predaceous  caterpillar  of  Lsetilia  coccidivora 
Comst.  has  been  an  efficient  ally  in  controlling  the 
pest  in  the  vicinity  of  Washington,  D.  C.  It  is 
particularly  effective  where  the  cottony  masses  are 
in  close  proximity,  because  of  its  habit  of  eating 
its  way  through  the  masses,  spinning  a  strong  web 
about  itself,  and  forming  a  gallery  as  it  progresses. 
The  caterpillar  is  very  active  and  moves  about 
freely  within  its  web. 

Several  specimens  of  Leucopis  nigricornis  Egger, 
a  common  dipterous  parasite  of  aphides,  were 
reared  from  cottony  maple  scale  collected  in 
Chicago,  111.,  on  July  21,  1905,  by  the  writer,  and 
from  other  specimens  sent  to  the  Bureau  from 
Crystal  Lake,  111.  This  parasite  is  considered  to  be 
a  European  species,  and  although  aphides  seem  to 
be  its  favorite  host,  it  is  occasionally  reared  from 
nondiaspine  Coccidae. 
Several  species  of  chalcid  flies  (Chalcidoidea)  are  truly  parasitic 
upon  the  cottony  maple  scale  as  well  as  upon  others  of  the  Lecaniina?. 
There  is  no  doubt  that  many  more  Pulvinarias  are  killed  by  these 
interesting  little  fellows  than  b}^  all  other  enemies.  Coccophag-us 
lecanii  Fitch,  C.  flavoscutellum  Ashm.,  Atropates  collinsi  How., 
Aphycus  pulvinarix  How.,  Corny s  fusca  How.,  and  Eunotus  lividus 
Ash m.  have  been  reared  from  the  cottony  maple  scale. 


Fig.  Z.—Pulvinaria  innu- 
merabilis:  Gravid  fe- 
male, greatly  enlarged, 
before  commencing  to 
secrete  egg  sac  in  the 
spring.  (From  Howard.) 


REMEDIES. 


Ill  dealing  with  an  infestation  by  the  cottony  maple  scale,  the  most 
important  matter  to  be  considered  in  each  case  is  the  advisability  of 

LCir.  G4.J 


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artificial  means  of  control  under  the  existing  conditions.  The  natural 
enemies  of  this  pest  have  done  and  are  still  doing  such  effective  work 
in  its  control,  that  it  is  a  question  whether  remedies  should  be  applied 
when  the  infestation  is  not  serious.  Nature  always  maintains  a 
balance,  and  this  pest  can  not  be  in  the  ascendency  for  any  great 
length  of  time.  On  the  contrary,  its  parasites  will  eventually 
multiply  so  rapidly  as  to  completely  check  its  progress,  and  it  may 
even  narrowly  escape  extermination. 

Insecticides  applied  for  a  pest  always  kill  its  parasites  and  often- 
times predaceous  enemies  are  also  destroyed.  Hundreds  of  larvae  of 
Hyperaspis  binotata  were  found  to  have  been  destroyed  by  a  summer 
treatment  with  kerosene  emulsion  for  the  cottony  maple  scale  in  parks 
of  Chicago,  and  no  doubt  thousands  of  the  minute  chalcids  were  killed, 
as  they  were  found  quite  plentifully  on  unsprayed  trees. 

If  it  is  necessary  to  resort  to  artificial  means  of  control,  as  seems  to 
be  the  case  in  some  sections,  the  spraying  should  be  delayed  until  fall 
or  winter,  when  the  Hyperaspis  is  hibernating  at  the  bases  of  the  trees 
among  lichens,  moss,  or  dried  grass. 
Care  should  be  exercised  in  the  use  of 
spray,  and  the  bases  of  trees  should 
be  covered  with  canvas  or  other  suit- 
able material  to  prevent  the  spray 
from  running  down  the  tree-trunks 
and  collecting  at  their  bases. 

WINTER   TREATMENT. 

When  the  trees  have  become  dor- 
mant, after  the  falling  of  the  leaves, 
they  can  be  trimmed  and  thoroughly 
sprayed  with  a  strong  kerosene  emul- 
sion, which  will  kill  every  scale  reached  by  the  spray,  without  injury 
to  the  trees.  Scarcely  one-fourth  the  quantity  of  emulsion  is  required 
to  spray  a  tree  in  winter  condition  that  is  necessary  when  a  tree  is 
covered  with  dense  foliage  and  both  sides  of  the  leaves  must  be 
reached  with  the  spray.  Some  excellent  results  have  been  obtained 
by  Mr.  S.  Arthur  Johnson1  in  experiments  against  this  pest  in 
Denver,  Colo.  He  found  that  kerosene  emulsion  25  per  cent  or  more 
in  strength  or  whale-oil  soap  at  the  rate  of  1  pound  to  1  gallon  of 
water  was  very  effective,  apparently  killing  all  scales  which  received 
the  spray. 

SUMMER   TREATMENT. 

Kerosene  emulsion  of  not  more  than  10  to  12  per  cent  of  oil  can  be 
thoroughly  applied  with  safety  to  maple  trees,  but  the  tips  and  mar- 


Fig.  4.— Hyperaspis  binotata:  a,  Adult;  6, 
antenna;  c,  palpus;  d,  larva.  Enlarged. 
(Original.) 


1  1905:  Bui.  52,  U.  S.  Dept.  Agr. 
[Cir.  64.] 


Bureau  of  Entomology,  pp.  85- 


gins  of  the  leaves  may  be  injured  even  at  this  strength.  Box-elder 
will  be  almost  defoliated  with  a  12  to  15  per  cent  solution.  Less  than 
a  10  per  cent  emulsion  will  be  of  little  value  against  the  young  unless 
they  have  recently  hatched.  Since  the  hatching  period  may  extend 
over  six  or  eight  weeks,  it  will  be  seen  that  more  than  one  spraying 
will  be  necessary  to  insure  success,  and,  coupled  with  the  fact  that  it 
is  a  very  difficult  and  disagreeable  task  to  thoroughly  spray  a  tree  in 
foliage,  the  winter  treatment  will  be  found  more  satisfactory  in  every 
way.  And  at  that  season  the  larvae  of  predaceous  beetles  would  not 
be  destroved. 


KEROSENE    EMULSION. 

Stock  solution  (66  per  cent  oil). 

Kerosene  (coal-oil,  lamp-oil) gallons. .  2 

Whale-oil  or  laundry  soap  (or  1  quart  soft  soap) pound. .  £ 

Water gallon. .  1 

Dissolve  the  soap  in  boiling  water,  then  remove  from  the  fire,  add  the 
kerosene  immediately  and  thoroughly  agitate  the  mixture  until  a 
creamy  solution  is  obtained.  This  can  be  done  by  pouring  the  mix- 
ture into  the  tank  of  a  spray-pump  and  pumping  the  liquid  through 
the  nozzle  back  into  the  tank.  This  is  a  stock  solution,  which  must 
be  diluted  before  using.  In  order  to  make  a  10  per  cent  emulsion, 
add  to  each  gallon  of  the  stock  solution  about  6  gallons  of  water  and 
agitate  thoroughly  before  using.  For  a  30  per  cent  solution  add  to 
each  gallon  of  the  stock  solution  1 J  gallons  of  water  and  agitate  thor- 
oughly. This  strength  will  kill  a  large  percentage  of  the  hibernating 
females,  without  injury  to  the  trees. 

If  a  good  naphtha  soap  can  be  obtained,  the  preparation  of  the 
emulsion  will  be  simplified.  It  will  be  unnecessary  to  heat  the  solu- 
tion, since  the  kerosene  will  combine  readily  with  the  naphtha  and 
soap  and  form  a  perfect,  cold,  milky- white  emulsion  when  the  mix- 
ture is  thoroughly  agitated.  If  naphtha  soap  is  used,  double  the 
amount  called  for  by  the  formula,  and  emulsify  in  soft  (rain)  water. 

Approved : 

James  Wilson, 

Secretary  of  Agriculture . 

Washington,  D.  C,  September  7,  1905. 

[Cir.  64.] 


o 


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